1. Field of the Invention
The present invention generally relates to a sewage collecting system. More particularly, the present invention relates to a vacuum type sewage collecting system for collecting sewage from a number of houses. In addition, the present invention relates to a controller for properly controlling opening/closing operations of a vacuum valve employable in the vacuum type sewage collecting system.
2. Description of the Related Art
A vacuum type sewage collecting system has been heretofore known for collecting sewage from a number of houses.
FIG. 3 is a schematic perspective view which shows the entire structure of a vacuum type sewage collecting system of the foregoing type.
As shown in the drawing, sewage discharged from houses 130 on the ground flows via a plurality of natural flow-down type sewer pipes 101 into a sewage reservoir 3 disposed underground. The sewage reservoir 3 has a vacuum valve 1 included therein. When a predetermined quantity of sewage has been collected in the sewage reservoir 3, it is sucked into a vacuum sewage pipe 110 via a suction pipe 5 and the vacuum valve 1, so as to be collected in a collecting tank 41 of a vacuum pump station 40. A constant level of vacuum in the collecting tank 41 is maintained by a pair of vacuum pumps 43. When a predetermined quantity of sewage has collected in the collecting tank 41, the sewage is further transferred to a sewer treating station or a like installation (not shown) by a pair of pumps 42.
FIG. 4 is a sectional view of the sewage reservoir 3 having the vacuum valve 1 therein.
As is apparent from the drawing, a controller 6 is mounted on the vacuum valve 1 to properly control opening/closing operations of the vacuum valve 1.
When a quantity of sewage in excess of a predetermined amount stored in a sewage reservoir 17 is detected by a sensor tube 4, a valve disc (not shown) is opened in the vacuum valve 1. In response to this detection, a suction pipe 5 is communicated with a vacuum sewage pipe 110 so that the sewage stored in the sewage reservoir 17 is sucked up into the suction pipe 5 under the influence of a vacuum which prevails throughout the vacuum sewage pipe 110.
Next, the structure and operation of the conventional vacuum valve controller 6 will be described below.
FIG. 5 is a sectional view which schematically illustrates an inner structure of the vacuum valve controller 6 as well as the vacuum valve 1. The structure of the conventional vacuum valve controller 6 is disclosed in U.S. Pat. No. 4,373,838.
The vacuum sewage pipe 110 is connected to a distributing chamber 61 via piping 62. Negative pressure outlet piping 63 is connected to a cylinder chamber la of the vacuum valve 1. A gas pressure introducing pipe 16 is connected to the sensor tube 4 shown in FIG. 4. An atmospheric pressure introducing hole 64 communicates with the outside environment via piping 65.
While the illustrated state (i.e., the state wherein a quantity of sewage less than a predetermined amount is stored in the sewage reservoir 17) is maintained, the negative pressure in the vacuum sewage pipe 110, which has been introduced into the controller 6 via the pipe 62, is delivered to a first vacuum chamber 70, piping 68 and a needle valve 69. A valve port 67 of the first vacuum chamber 70 is normally closed by a valve 66. In addition, the negative pressure is also delivered to a second vacuum chamber 73 via the piping 68, an orifice 71, and piping 72.
At this time, the interior of the first vacuum chamber 70 and the interior of the second vacuum chamber 73 are held at the same negative pressure, respectively, and a valve stem 76 having a diaphragm 75 fixedly secured thereto is displaced to an ultimate position on the left-hand side by a coil spring 74.
Further, the atmospheric pressure which has been introduced into the controller 6 via the piping 65 is delivered to a cylinder chamber 1a of the vacuum valve 1 via piping 63. A valve disc 1c fixedly secured to a piston 1b is brought into contact with a valve seat 1e under the atmospheric pressure and the resilient force of a coil spring 1d, whereby communication between the vacuum sewage pipe 110 and the suction pipe 5 is interrupted.
As an increasing amount of sewage is stored in the sewage reservoir 17 (see FIG. 4) and the depth of the stored sewage increases, the gas pressure in the sensor tube 4 correspondingly increases. This causes the pressure in a pressure detecting chamber 77, communicated with the sensor tube 4, to increase, whereby a diaphragm 78 defining the pressure detecting chamber 77 is displaced in the rightward direction as viewed in FIG. 5.
At this time, a projection 79 on the diaphragm 78 is likewise displaced in the rightward direction until it comes into contact with one end of a lever 80 and is thrust against the latter.
Then, the lever 80 turns about a hinge 81 in a clockwise direction so that a valve 82 on the other end of the lever 80 opens a valve port 83.
When the valve port 83 is opened, the atmospheric pressure in an atmospheric pressure chamber 85 communicated with the piping 65, the atmospheric pressure introducing hole 64, and a passage 84, is introduced into the first vacuum chamber 70.
As a result, a differential pressure is established between the second vacuum chamber 73 held in the negative pressure state and the first vacuum chamber 70 held in the atmospheric pressure state, whereby a diaphragm 75 is displaced against the resilient force of the coil spring 74 in the rightward direction. Thus, the valve stem 76 fixedly secured to the diaphragm 75 is displaced in the rightward direction so that the valve 66 interrupts the communication between the atmospheric pressure hole 64 and the piping 63 and simultaneously establishes the communication between the distributing chamber 61 and the piping 63.
For this reason, the negative pressure in the vacuum sewage pipe 110 is introduced into the cylinder chamber 1a of the vacuum valve 1 via the piping 62, the distributing chamber 61, the valve port 67, and the piping 63. This causes the piston 1b and the valve disc 1c to be raised up against the resilient force of the coil spring 1d, whereby the suction pipe 5 is communicated with the vacuum sewage pipe 110.
Then, the sewage stored in the sewage reservoir 17 shown in FIG. 4 is sucked into the vacuum sewage pipe 110 via the suction pipe 5.
As shown in FIG. 5, the piping 62 is connected to the vacuum sewage pipe 110 at a location in the vicinity of the vacuum valve 1. Therefore, when the suction pipe 5 is communicated with the vacuum sewage pipe 110, there is a possibility that the pressure prevailing in the connection region will be raised to a level near the atmospheric pressure. To avoid the foregoing possibility, a check valve 199 is disposed in the piping 62 and a check valve 86 is additionally disposed in the piping 68. Therefore, air having a pressure near to atmospheric pressure is never introduced into the first vacuum chamber 70 and the second vacuum chamber 73.
Next, as the quantity of sewage in the sewage reservoir 17 decreases, the gas pressure in the sensor tube 4 and the pressure detecting chamber 77 decreases and the differential pressure between the pressure detecting chamber 77 and the atmospheric pressure chamber 85 decreases. Then, the diaphragm 78 is restored to its original position, whereby the lever 80 is released from the thrusting state induced by the projection 79, and the valve port 83 is closed with the valve 82.
Thereafter, air in the first vacuum chamber 70 held at the atmospheric pressure is gradually displaced to the second vacuum chamber 73 via the piping 68, the needle valve 69, an orifice 71, and piping 72, while it is likewise gradually displaced to the distributing chamber 61 via check valve 86.
As the differential pressure between the first vacuum chamber 70 and the second vacuum chamber 73 gradually disappears, the diaphragm 75 is gradually restored to its original state. Thus, owing in part to the resilient force of coil spring 74, the valve stem 76 is restored to its original position at which the valve port 67 is closed with the valve 66.
When the atmospheric pressure introducing hole 64 is communicated with the piping 63, the atmospheric pressure is introduced into the cylinder chamber 1a so that the negative pressure which has raised the piston 1b disappears. As a result, the valve disc 1c is closed under the resilient force of the coil spring 1d.
It should be noted that the vacuum valve 1 is kept open for a predetermined period of time without the valve stem 76 being restored to the original position due to the differential pressure between the first vacuum chamber 70 and the second vacuum chamber 73, i.e. during the time when the gas pressure in the sensor tube 4 and the pressure detecting chamber 77 is reduced and the valve port 83 is closed with the valve. This is intended to additionally suck air into the sewage reservoir 17 after sewage water is sucked through the suction pipe 5, because suction of the air in this way causes the sewage and the air to be mixed together in the vacuum sewage pipe 110 in a slag flow state or a plug flow state, resulting in an increased efficiency of transportation of the sewage.
To properly adjust a period of time that elapses until the vacuum valve 1 is closed, i.e. to properly adjust a volume of air to be sucked into the vacuum sewage pipe 110, it is required that the opening of the needle valve 69 is adequately selected to establish an appropriate displacement of the gas from the first vacuum chamber 70 to the second vacuum chamber 73.
With the conventional vacuum valve controller 6 as constructed in the above-described manner, since the piping 62 is connected to a joint on the vacuum sewage pipe 110 in the vicinity of the vacuum valve 1, the negative pressure in the joint region is reduced (to a level approximately equal to the atmospheric pressure) and a negative pressure to be fed to the vacuum valve controller 1 is unavoidably reduced in a case where the vacuum sewage pipe 110 is long or an air lock occurs at an intermediate part of the vacuum sewage pipe 110.
For this reason, when the valve port 83 of the vacuum valve controller 6 is opened, causing the pressure in the first vacuum chamber 70 to be equalized to the atmospheric pressure, the differential pressure between the first vacuum chamber 70 and the second vacuum chamber 73 becomes small, since the second vacuum chamber 73 has a low negative pressure. Therefore, the diaphragm 75 is restored to its original state merely by the displacement of a small volume of air from the first vacuum chamber 70 to the second vacuum chamber 73 with the result that the vacuum valve 1 is closed within a period of time shorter than that in the normal case.
Specifically, when the negative pressure in the vacuum sewage pipe 110 is reduced for some reason, the vacuum valve 1 is closed earlier than in the normal case, whereby a small volume of air is sucked into the vacuum sewage pipe 110 and a ratio of gas to liquid in the vacuum sewage pipe 110 becomes small, resulting in a predisposition to the formation of air locks. Consequently, there repeatedly occurs a malfunction in that the negative pressure in the vacuum sewage pipe 10 is gradually reduced more and more and a volume of air to be sucked into the vacuum sewage pipe 110 gradually becomes less.